On farms, the transfer of granular foodstuffs such as grain, corn kernels, beans, and the like from, for example, a storage bin to a transport trailer, is frequently carried out using a trailer-mounted pneumatic conveying system. A typical conveying system will be mounted on a wheeled frame adapted to be towed behind a tractor, which also provides the power source for the system. The majority of conveyor systems include a vacuum source for drawing the granular material, such as grain, entrained in a first air stream from a first location through a flexible inlet conduit into a cyclone separator. The grain falls to the bottom of the separator while the entraining air passes through an opening in the upper part of the separator leading to the vacuum source. In many existing conveyor systems, the vacuum source is a Rootes-type positive displacement blower, producing a vacuum on the upstream side of the blower, while also, on the downstream side, acting as a pressure source providing a second air stream for pushing the grain from a rotating, vaned valve at the base of the separator. The grain is entrained in this air stream and accelerated from the valve into an outlet conduit, which extends from the valve to an elevated grain outlet. Conveniently, power for the blower is taken through a system of belts from the tractor power take-off, while the rotating valve is driven by a hydraulic motor from the hydraulic system of the tractor.
The ratio of air to entrained grain is important in achieving a smooth flow through the conveyor: if not enough air is present the grain may plug the flexible inlet conduit or the oulet conduit; and if too much air is present the conveyor will operate inefficiently, that is, moving grain at a lower rate than is possible at the optimum air to grain ratio. The amount of air passing through the conveyor is normally controlled by an air valve adjacent the mouth of the inlet conduit.
The optimum operating ratio of air to entrained grain for a particular system is governed by a wide variety of system characteristics, including air "leakage" and internal configuration. Air leakage occurs at various points along the grain path, particularly in the flexible inlet conduit and the outlet conduit, if it includes flexible portions. This is in part due to the use of flexible tubing formed of interlocked stainless steel spirals to form the flexible portions. When new, leakage through the flexible tubing is negligible, however, damage sustained through usage leads to deterioration of the integrity of the tubing, and increased leakage.
As mentioned above, conveyor systems are normally trailer-mounted for easy transporting, or towing, between sites. Accordingly, the system and trailer must conform to public highway width and height restrictions. During grain transfer operations, the boom section of the outlet conduit extends from the trailer to the grain outlet, which may be 12-13' above ground level and a similar distance from the side or rear of the trailer. The boom section must therefore be rectractable for towing. This may be achieved in one of several ways: the outlet conduit may comprise a detachable flexible lower section and rigid upper boom section which may be pivoted to a towing position in which the boom section extends, for example, diagonally across the trailer and is supported by a bracket on an upper portion of the separator, the lower section being detached from the air lock and boom section and stowed on the trailer; or alternatively, the outlet conduit may comprise two hinged rigid sections such that the conduit may be "broken" in two for towing. With the former configuration, the operator must detach and attach the flexible lower section each time the conveyor is moved between sites. The continual handling of the section tends to cause deterioration and the detached section is vulnerable to damage. The latter configuration generally has greater durability but does not permit for height adjustment of the grain outlet, which can present problems, for example, in windy conditions when a lower than average trailer is being loaded.
The overall configuration of the conveyor system on a trailer also influences the form of outlet conduit, as the lower section of boom initially lies horizontally, to receive grain from the air lock at a lower portion of the trailer, and from a horizontal orientation extends to a substantially upright orientation adjacent to the join with the upper boom section. This transition must be accommodated within the restricted dimensions of the trailer.